Is a non-blocking, single-threaded, asynchronous w

Question

I was looking at this question, looking for a way to create a single-threaded, event-based nonblocking asynchronous web server in .NET.

This answer looked promising at first, by claiming that the body of the code runs in a single thread.

However, I tested this in C#:

using System;
using System.IO;
using System.Threading;

class Program
{
    static void Main()
    {
        Console.WriteLine(Thread.CurrentThread.ManagedThreadId);

        var sc = new SynchronizationContext();
        SynchronizationContext.SetSynchronizationContext(sc);
        {
            var path = Environment.ExpandEnvironmentVariables(
                @"%SystemRoot%\Notepad.exe");
            var fs = new FileStream(path, FileMode.Open,
                FileAccess.Read, FileShare.ReadWrite, 1024 * 4, true);
            var bytes = new byte[1024];
            fs.BeginRead(bytes, 0, bytes.Length, ar =>
            {
                sc.Post(dummy =>
                {
                    var res = fs.EndRead(ar);

                    // Are we in the same thread?
                    Console.WriteLine(Thread.CurrentThread.ManagedThreadId);
                }, null);
            }, null);
        }
        Thread.Sleep(100);
    }
}

And the result was:

1
5

So it seems like, contrary to the answer, the thread initiating the read and the thread ending the read are not the same.

So now my question is, how do you to achieve a single-threaded, event-based nonblocking asynchronous web server in .NET?

Answer 1

I believe it's possible, here is an open-source example written in VB.NET and C#:

https://github.com/perrybutler/dotnetsockets/

It uses Event-based Asynchronous Pattern (EAP), IAsyncResult Pattern and thread pool (IOCP). It will serialize/marshal the messages (messages can be any native object such as a class instance) into binary packets, transfer the packets over TCP, and then deserialize/unmarshal the packets at the receiving end so you get your native object to work with. This part is somewhat like Protobuf or RPC.

It was originally developed as a "netcode" for real-time multiplayer gaming, but it can serve many purposes. Unfortunately I never got around to using it. Maybe someone else will.

The source code has a lot of comments so it should be easy to follow. Enjoy!

Answer 2

First about SynchronizationContext. It's just like Sam wrote. Base class won't give You single-thread functionality. You probably got that idea from WindowsFormsSynchronizationContext which provides functionality to execute code on UI thread.

You can read more here

I've written a piece of code that works with ThreadPool parameters. (Again something Sam already pointed out).

This code registers 3 asynchronous actions to be executed on free thread. They run in parallel until one of them changes ThreadPool parameters. Then each action is executed on the same thread.

It only proves that you can force .net app to use one thread. Real implementation of web server that would receive and process calls on only one thread is something entirely different :).

Here's the code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.IO;

namespace SingleThreadTest
{
    class Program
    {
        class TestState
        {
            internal string ID { get; set; }
            internal int Count { get; set; }
            internal int ChangeCount { get; set; }
        }

        static ManualResetEvent s_event = new ManualResetEvent(false);

        static void Main(string[] args)
        {
            Console.WriteLine(Thread.CurrentThread.ManagedThreadId);
            int nWorkerThreads;
            int nCompletionPortThreads;
            ThreadPool.GetMaxThreads(out nWorkerThreads, out nCompletionPortThreads);
            Console.WriteLine(String.Format("Max Workers: {0} Ports: {1}",nWorkerThreads,nCompletionPortThreads));
            ThreadPool.GetMinThreads(out nWorkerThreads, out nCompletionPortThreads);
            Console.WriteLine(String.Format("Min Workers: {0} Ports: {1}",nWorkerThreads,nCompletionPortThreads));
            ThreadPool.QueueUserWorkItem(new WaitCallback(LetsRunLikeCrazy), new TestState() { ID = "A  ", Count = 10, ChangeCount = 0 });
            ThreadPool.QueueUserWorkItem(new WaitCallback(LetsRunLikeCrazy), new TestState() { ID = " B ", Count = 10, ChangeCount = 5 });
            ThreadPool.QueueUserWorkItem(new WaitCallback(LetsRunLikeCrazy), new TestState() { ID = "  C", Count = 10, ChangeCount = 0 });
            s_event.WaitOne();
            Console.WriteLine("Press enter...");
            Console.In.ReadLine();
        }

        static void LetsRunLikeCrazy(object o)
        {
            if (s_event.WaitOne(0))
            {
                return;
            }
            TestState oState = o as TestState;
            if (oState != null)
            {
                // Are we in the same thread?
                Console.WriteLine(String.Format("Hello. Start id: {0} in thread: {1}",oState.ID, Thread.CurrentThread.ManagedThreadId));
                Thread.Sleep(1000);
                oState.Count -= 1;
                if (oState.ChangeCount == oState.Count)
                {
                    int nWorkerThreads = 1;
                    int nCompletionPortThreads = 1;
                    ThreadPool.SetMinThreads(nWorkerThreads, nCompletionPortThreads);
                    ThreadPool.SetMaxThreads(nWorkerThreads, nCompletionPortThreads);

                    ThreadPool.GetMaxThreads(out nWorkerThreads, out nCompletionPortThreads);
                    Console.WriteLine(String.Format("New Max Workers: {0} Ports: {1}", nWorkerThreads, nCompletionPortThreads));
                    ThreadPool.GetMinThreads(out nWorkerThreads, out nCompletionPortThreads);
                    Console.WriteLine(String.Format("New Min Workers: {0} Ports: {1}", nWorkerThreads, nCompletionPortThreads));
                }
                if (oState.Count > 0)
                {
                    Console.WriteLine(String.Format("Hello. End   id: {0} in thread: {1}", oState.ID, Thread.CurrentThread.ManagedThreadId));
                    ThreadPool.QueueUserWorkItem(new WaitCallback(LetsRunLikeCrazy), oState);
                }
                else
                {
                    Console.WriteLine(String.Format("Hello. End   id: {0} in thread: {1}", oState.ID, Thread.CurrentThread.ManagedThreadId));
                    s_event.Set();
                }
            }
            else
            {
                Console.WriteLine("Error !!!");
                s_event.Set();
            }
        }
    }
}

Answer 3

you can this framework SignalR and this Blog about it

Answer 4

Yes, it's called Manos de mono

Seriously, the entire idea behind manos is a single threaded asynchronous event driven web server.

High performance and scalable. Modeled after tornadoweb, the technology that powers friend feed, Manos is capable of thousands of simultaneous connections, ideal for applications that create persistent connections with the server.

The project appears to be low on maintenance and probably wouldn't be production ready but it makes a good case study as a demonstration that this is possible.

Answer 5

I developed a server based on HttpListener and an event loop, supporting MVC, WebApi and routing. For what i have seen the performances are far better than standard IIS+MVC, for the MVCMusicStore i moved from 100 requests per seconds and 100% CPU to 350 with 30% CPU. If anybody would give it a try i am struggling for feedbacks! Actually is present a template to create websites based on this structure.

Note that I DON'T USE ASYNC/AWAIT until absolutely necessary. The only tasks i use there are the ones for the I/O bound operations like writing on the socket or reading files.

PS any suggestion or correction is welcome!

• Documentation
• MvcMusicStore sample port on Node.Cs
• Packages on Nuget

Answer 6

Here's a great article series explaining what IO Completion Ports are and how they can be accessed via C# (i.e. you need to PInvoke into Win32 API calls from the Kernel32.dll).

Note: The libuv the cross platform IO framework behind node.js uses IOCP on Windows and libev on unix operating systems.

http://www.theukwebdesigncompany.com/articles/iocp-thread-pooling.php